Special thanks to Eric Bléher for providing this lens for testing purposes!

Introduction

The Sigma AF 50mm f/1.4 EX DG HSM is a quite uncommon lens. It is Sigma's first-ever large aperture AF 50mm lens which is quite surprising regarding the market significance of the company. However, it seems as if Sigma is aware of the market potential because they're going to release the AF 85mm f/1.4 EX DG HSM in Q3/2010. It seems as of that the 50mm lens species is generally ready for a revival thanks to APS-C DSLRs where the field-of-view is equivalent to 80mm (1.6x crop) - a pretty sweet spot for portrait photography. Unlike other full format 50mm f/1.4 lenses it features a massive front element (77mm filter thread) and it takes advantage of an aspherical element and both aspects are pretty unique design decisions for a 50mm f/1.4 lens. Sigma is obviously quite confident regarding their new baby because they are bold enough to ask a street price beyond the other 50mm f/1.4 AF lenses - around 400€/480US$.

The build quality of the Sigma lens is excellent - the outer body is obviously made of some kind of metal applied with the typical Sigma EX coating (crinkle finish). The focus ring operates very smooth. Unlike most 50s it has a constant physical length regardless of the focus setting although the inner lens tube moves a little.

The HSM ("Hyper-Sonic-Motor") AF is very fast and virtually silent. AF accuracy is a difficult topic for the Sigma. It seems to suffer from pronounced focus shifts when stopping down ("Residual spherical aberrations") which is probably the reason why many users report back- or front-focusing issues.